This invention relates to a printing apparatus and an ink-discharge status detection method, and more particularly, to a printing apparatus having a printhead, including a plurality of nozzles, to perform printing in accordance with an ink-jet method, and an ink-discharge status detection method used in the printing apparatus.
A printer which performs printing in accordance with the ink-jet method has a plurality of fine nozzles integrated in a high density. The printer directly discharges ink from the nozzles onto a print medium, thus forms an image by the ink dots. If impurities (dust) enter a nozzle, the ink adheres to a portion around the ink discharge orifice, or the nozzle is clogged with the impurities or the adhered ink, ink discharge failure may occur. Further, in a method of heating ink to cause film boiling and discharge the ink by the pressure of bubbles produced in a nozzle (so-called bubble-jet method), ink discharge failure may occur if disconnection occurs in a heater of the nozzle.
The ink discharge failure considerably degrades the quality of a printed image. Especially, in a production-material manufacturing apparatus such as an apparatus used for textile printing which requires very high image quality, the discharge failure is a serious problem which might lower the reliability of the apparatus.
Conventionally, a several methods have been proposed as follows to detect the discharge failure status.
(1) A print medium for detecting ink-discharge status is provided outside of an effective printing area by a printhead. Then, a pattern enabling discrimination of a nozzle in discharge failure status is printed on the print medium. Next, the pattern is optically read by using an optical reader such as a CCD camera, and a nozzle in the discharge failure status, if exists, is determined. In this case, the optical reader can be moved to the position of the print medium, otherwise, a disk or roller-shaped print medium may be used such that the print medium can be rotated to the position of the optical reader.
(2) A light emitting device is provided such that a light beam emitted from the device passes through an area outside of an effective printing area by a printhead. Then, a printhead is stopped around the light axis of the light beam, and ink is discharged to block the light beam. The light beam is received by a photoreception device provided at a position opposite to the light emitting device, and it is determined whether or not discharge failure has occurred based on output from the photoreception device. According to this method, in use of a color printhead having a plurality of nozzle arrays corresponding to a plurality of color ink, the detection must be performed for the number of the nozzle arrays (the number of ink colors).
However, in the above conventional techniques, the print medium for detection or the optical reader must be moved for the discharge failure detection, or the printhead must be moved in a complicated manner different from that in normal print operation for the discharge failure detection. Accordingly, the apparatus must comprise a complicated mechanism, and further, the total printing speed of the apparatus is reduced.
Accordingly, it is an object of the present invention to provide a printing apparatus and an ink-discharge status detection method to detect discharge failure status and perform appropriate print control with a simple construction, without reducing the printing speed.
According to one aspect of the present invention, the foregoing object is attained by providing a printing apparatus which performs printing by discharging ink onto a print medium while scanning a printhead, based on an ink-jet method, having a plurality of printing elements, the apparatus comprising: scan means for scanning the printhead; print means for performing print operation by using the printhead; test discharge means for controlling operation of the printhead to select at least a part of the plurality of printing elements and perform test ink discharge while the scan means scans the printhead; detection means for detecting ink-discharge statuses of the plurality of printing elements of the printhead from the test ink discharge by the test ink discharge means; and first control means for controlling the test discharge means to sequentially select the printing elements of the printhead at each of plural scannings of the printhead by the scan means, and controlling the detection means to detect the ink-discharge statuses.
Note that it is preferable that the detection means is provided between a home position of the printhead, at one end of a scanning path of the printhead, and a position outside of an effective printing area for the printhead.
Further, it is preferable that the test discharge means includes: first test discharge means for controlling the operation of the printhead to select a part of the plurality of printing elements and perform test ink discharge while the scan means scans the printhead in a forward direction; and second test discharge means for controlling the operation of the printhead to select another part of the plurality of printing elements, different from the part of the printing elements selected by the first test discharge means, and perform ink discharge while the scan means scans the printhead in a backward direction.
Further, it is preferable that the apparatus further comprises: analysis means for detecting ink discharge statuses obtained by the first and second test discharge means by using the detection means, and analyzing operation statuses of the plurality of printing elements of the printhead based on the results of detection; and second control means for controlling the print operation by the print means, based on the analysis result.
Note that it is preferable that the plurality of printing elements of the printhead are arrayed in one line, and the detection means includes: light emission means for emitting a light beam; and photoreception means for receiving the light beam, and that the printhead is provided such that ink droplets discharged from the plurality of printing elements block the light beam. Further, it is preferable that the light emission means and the photoreception means are provided such that a light axis of the light beam intersects an array direction of the plurality of printing elements of the printhead.
Further, it may be arranged such that the ink discharge statuses of all of the plurality of printing elements of the printhead can be detected by operating the first and second test discharge means totally a predetermined number of times.
Further, it may be arranged such that the test discharge means uses a control signal the same as that used by the print means, and performs the ink discharge only by changing image data and timing for ink discharge. Further, it is preferable that a moving speed of the printhead while the test discharge means operates and that while the print means performs the print operation are the same.
Further, it may be arranged such that the printhead is a color printhead which discharges ink of plural colors, and which has a plurality of printing element arrays each comprising the plurality of printing elements corresponding to the plural colors. In this case, the plurality of printing elements selected by the test discharge means are determined based on a distance between the plurality of printing element arrays, a moving speed of the printhead, the number of printing elements consisting the plurality of printing element arrays, the length of printing by each of the plurality of printing element arrays, a printing resolution in a printhead scanning direction, an ink discharge period in the printhead scanning direction, and a distance between the printing elements of the printing element arrays.
Note that the printhead is an ink-jet printhead having discharge nozzles to discharge ink, respectively corresponding to the plurality of printing elements, and preferably, the printhead has electrothermal transducers for generating thermal energy to be provided to ink so as to discharge the ink by utilizing the thermal energy.
According to another aspect of the present invention, the foregoing object is attained by providing an ink-discharge status detection method used upon printing by discharging ink onto a print medium while scanning a printhead, based on an ink-jet method, having a plurality of printing elements, the method comprising: a test discharge step of controlling operation of the printhead to select at least a part of the plurality of printing elements and perform test ink discharge while scanning the printhead; a detection step of detecting ink-discharge statuses of the plurality of printing elements of the printhead based on the test ink discharge at the test ink discharge step; and a control step of controlling execution of the test discharge step to sequentially select the printing elements of the printhead at each of plural scannings of the printhead, and controlling execution of the detection step to detect the ink-discharge statuses.
Note that it is preferable that the detection step is performed when the printhead is situated between a home position of the printhead, at one end of a scanning path of the printhead, and a position outside of an effective printing area for the printhead.
In accordance with the present invention as described above, the ink-discharge status detection is performed such that ink is discharged onto a print medium while the printhead, based on the ink-jet method, having the plurality of printing elements is scanned. When the printhead is scanned, the operation of the printhead is controlled to perform test ink discharge from at least a part of the printing elements. For example, ink-discharge statuses of the plurality of printing elements of the printhead are detected, based on test ink discharge performed at an area between the home position of the printhead at one end of the scanning path of the printhead and a position outside of the effective printing area for the printhead. The test ink discharge is performed such that a predetermined number of printing elements are sequentially selected from the printing elements of the printhead at each scanning of a plural number of scannings and test discharge is performed.
The invention is particularly advantageous since the ink-discharge status detection can be implemented in the process of normal print operation without causing the printhead to perform any specific operation.
Accordingly, the ink-discharge status detection can be efficiently performed with a simple construction, without reducing the printing speed and without using a specific print control or mechanism. Further, the present invention omits conventionally required various mechanisms for ink-discharge status detection, thus contributing to the downsizing and the reduction of production cost.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.